The present invention relates to golf balls and more particularly, the invention is directed to improving the control of the spin rate of golf balls and to a method for varying the spin rate of golf balls.
The spin rate of golf balls is the end result of many variables, one of which is the distribution of the density or specific gravity within the ball. Spin rate is an important characteristic of golf balls for both skilled and recreational golfers. High spin rate allows the more skilled players, such as PGA professionals and low handicapped players, to maximize control of the golf ball. A high spin rate golf ball is advantageous for an approach shot to the green. The ability to produce and control back spin to stop the ball on the green and side spin to draw or fade the ball substantially improves the player""s control over the ball. Hence, the more skilled players generally prefer a golf ball that exhibits high spin rate.
On the other hand, recreational players who cannot intentionally control the spin of the ball generally do not prefer a high spin rate golf ball. For these players, slicing and hooking are the more immediate obstacles. When a club head strikes a ball, an unintentional side spin is often imparted to the ball, which sends the ball off its intended course. The side spin reduces the player""s control over the ball, as well as the distance the ball will travel. A golf ball that spins less tends not to drift off-line erratically if the shot is not hit squarely off the club face. The low spin ball will not cure the hook or the slice, but will reduce the adverse effects of the side spin. Hence, recreational players prefer a golf ball that exhibits low spin rate.
Reallocating the density or specific gravity of the various layers or mantles in the ball is an important means of controlling the spin rate of golf balls. In some instances, the weight from the outer portions of the ball is redistributed to the center of the ball to decrease the moment of inertia thereby increasing the spin rate. For example, U.S. Pat. No. 4,625,964 discloses a golf ball with a reduced moment of inertia having a core with specific gravity of at least 1.50 and a diameter of less than 32 mm and an intermediate layer of lower specific gravity between the core and the cover. U.S. Pat. No. 5,104,126 discloses a ball with a dense inner core having a specific gravity of at least 1.25 encapsulated by a lower density syntactic foam composition. U.S. Pat. No. 5,048,838 discloses another golf ball with a dense inner core having a diameter in the range of 15-25 mm with a specific gravity of 1.2 to 4.0 and an outer layer with a specific gravity of 0.1 to 3.0 less than the specific gravity of the inner core. U.S. Pat. No. 5,482,285 discloses another golf ball with reduced moment of inertia by reducing the specific gravity of an outer core to 0.2 to 1.0.
In other instances, the weight from the inner portion of the ball is redistributed outward to increase the moment of inertia thereby decreasing the spin rate. U.S. Pat. No. 6,120,393 discloses a golf ball with a hollow inner core with one or more resilient outer layers, thereby giving the ball a soft core, and a hard cover. U.S. Pat. No. 6,142,887 discloses an increased moment of inertia golf ball comprising one or more mantle layers made from metals, ceramic or composite materials, and a polymeric spherical substrate disposed inwardly from the mantle layers.
These and other references disclose specific examples of high and low spin rate ball with ranges of specific gravity, ranges of diameter for the core and ranges of thickness for the outer layers, etc. They, however, do not offer any universal guidelines to control the spin rate of golf balls. Hence, there remains a need in the art for an improved golf ball with controlled spin rates.
The present invention is directed to a golf ball with a controlled moment of inertia.
The present invention is also directed to a golf ball with a controlled spin rate.
The present invention is further directed to a method for controlling the moment of inertia of a golf ball.
The present invention is preferably directed to a ball comprising a core and a cover wherein the weight or mass of the ball is allocated radially relative to the centroid, thereby dictating the moment of inertia of the ball. When the weight is allocated radially toward the centroid, the moment of inertia is decreased, and when the weight is allocated outward away from the centroid, the moment of inertia is increased. A method for determining the centroid radius is also provided.
In accordance to one aspect of the invention, a low moment of inertia ball comprises a dense inner core having a specific gravity of at least higher than 1.8 encased by a low specific gravity layer, which has its specific gravity reduced by an agent. The specific gravity layer has a specific gravity of at least less than 0.9. The ball may also have an additional intermediate mantle and a cover. The core can be made from any high density material and can be solid or hollow. The core is preferably disposed radially inside of the centroid radius.
In accordance to another aspect of the invention, a high moment of inertia ball comprises a thin dense layer encasing an inner core. The thin dense layer has a specific gravity of at least greater than 1.2 and a thickness from 0.001 to 0.050 inch, and the outer surface of the thin dense layer is located at a distance ranging from 0.030 inch to 0.110 inch from the land surface. The thin dense layer is preferably located radially outside of the centroid radius.